The present invention relates to an apparatus for rocking a crank used both coil spring made of the shape memory alloy and bias coil spring or coil spring made of the shape memory alloy, which functions particularly to increase the rocking stroke of the crank and/or the rotational angle of the crank axis.
The shape memory alloy is one which shows an unique characteristic called the shape memory effect, that is, when the alloy is made to memorize a definite shape at a high temperature and then deformed at a temperature below the transformation temperature, it recovers the memorized shape on heating above the transformation temperature, and the alloys of the types of Ni-Ti, Cu-Zn-Al, Au-Cd and the like are known. The phenomenon called the shape memory effect is an irreversible phenomenon ordinarily. Although the alloy recovers the memorized shape on heating after deformed at a low temperature, it does not rerecover the shape deformed at the low temperature, even if cooled it to the low temperature again. In order to utilize this phenomenon industrially, it is necessary to make the alloy function reversible that enables repetitive action, and various methods have been proposed. Among these methods, a method by means of bias force has the advantages that the design of the device is easy, that not large amount of the shape memory alloy material are needed, etc., and a method by means of differential motion has the advantages that the generating force is strong, that the control of the generating force is easy, etc. Therefore, both methods are used widely.
The method by means of bias force or differential motion utilizes the characteristics that the shape memory alloy is soft and the yield stress is small at a low temperature, that is, a temperature lower than that of the shape being recovered by heating (this is called Af point), while it is hard and the yield stress is large at a high temperature above the Af point. for example, as shown in FIG. 1, an apparatus is known, wherein a rod (3) is made to be pulled to and fro by placing coil spring made of the shape memory alloy (1) (hereinafter abbreviated to as F spring) and bias coil spring or coil spring made of the shape memory alloy (2) (hereinafter abbreviated to as B spring) under a state of pulling deformation appropriately. In the case of the method by means of bias force using bias coil spring as described above, the shape memory alloy is soft at a temperature below the Af point. Therefore, the F spring (1) is pulled and extended by the B spring (2) and the rod (3) occupies a position at the side of B spring (2). When the temperature is raised to a temperature above the Af point by heating through the irradiation with infrared rays, the conduction of electric current and the like, the F spring (1) becomes hard and strong as well as it recovers the memorized shape. Therefore, the rod (3) is pulled by F spring (1) to move to the side of F spring (1). When the temperature of the F spring (1) is lowered again to a temperature below the Af point, the F spring (1) becomes soft and the rod (3) moves to the side of B spring (2) as a result of the pulling by B spring (2). Therefore, the rod (3) becomes to be subjected to the reciprocative movement through the shape change due to the temperature variation, and this is utilized to various actuators.
On the other hand, in the case of the method by means of differential motion using coil spring made of the shape memory alloy (B spring) as described above, if the temperature of the B spring (2) is raised to a temperature above the Af point by heating through the irradiation with infrared rays, the conduction of electric current and the like under a state that the ambient temperature is lower than the Af point, the B spring (2) becomes hard and strong as well as it recovers the shape, while the F spring (1) is soft remaining at a temperature below the Af point. Therefore, the F spring (1) is pulled and extended by B spring (2) and the rod (3) moves to the side of B spring (2). When stopped the heating of the B spring (2) and heated the F spring (1), the F spring (1) becomes hard and strong as well as it recovers the shape this time and pulls the B spring (2). While the B spring (2) which is not heated becomes soft remaining at a temperature below the Af point and is pulled by F spring (1). As a result, the rod (3) moves to the side of F spring (1). Therefore, the rod (3) becomes to be subjected to the reciprocative movement through the shape change due to the temperature variation of both springs of F (1) and B (2), and this is utilized similarly to various actuators.
However, with the structure as this, when the F spring contracts from the extended state through the shape recovery, the shape recovery force is decreased gradually as the contraction of the F spring proceeds, while the spring force of the B spring is increased gradually as the B spring is pulled and extended. As a result, the generating force which is a difference between the forces of both springs is to be decreased rapidly with an increase of the rod movement (stroke). In order to increase the stroke and the generating force, it is necessary to decrease the stroke dependence of the force of the B spring and the shape recovery force of the F spring. For the attainment of this, both springs become long, and there have been the problems in the points of the size of the apparatus, price, etc.
In order to dissolve this, such one is known as contrived in a manner that the spring force of the B spring is not increased but decreased adversely on the contraction of the F spring through the shape recovery by utilizing the crank mechanism and making the B spring have a negative spring force dependence apparently. For example, in the disclosure of Japanse Unexamined Patent Publication No. 7683/1974, the moment brought by the B spring is arranged to have a negative position dependence constantly. Since the moment is a product of the distance with the force, if the variation of the distance is large enough compared with that of the force and has a negative dependence, the negative position dependence can be obtained as a whole moment to compensate for a positive position dependence of the shape recovery force of shape memory alloy. However, as shown in FIG. 2(A), in order to make the moment brought by the B spring exhibit a negative variation against the position of the crank (4) and generate an effective force, the range of the angle is extremely narrow as shown by A in FIG. 2(B), and it has been impossible to make the stroke long.
As a result of various investigations in view of this, an apparatus for rocking the crank has been developed leading to the invention, which has made it possible to obtain a strong generating force in a wide position ranging by improving the crank mechanism, and by making the position dependence of the moment brough by the B spring negative within the position range where the moment brought by the F spring has a positive dependence against the position and the position dependence of the moment of B spring positive within the position range where the moment of F spring has a negative position dependence.